Amber Listserv / Amber Care and Disintegration of Sphecomyrma freyi -

Sun Mar 11 09:35:52 EDT 2007

Chris, note the below:

APPENDIX

Vacuum Embedding and Disintegration
of the Type of Sphecomyrma freyi
The holotype of Sphecomyrma freyi occurrec
in a deep red piece of amber collected in 196(
from Cliffwood Beach, New Jersey. The piece
originally contained two workers, but it cracked,
separating the two workers (Wilson et al.,
1967a,b). The piece containing the holotype (photograph
in Holldobler and Wilson, 1990) was
roughly cubical, approximately 22 X 18 X 17
mm, very brittle, with some fine, superficial
cracks; larger cracks permeated deeply into the
piece. It was stored in a wooden cabinet in an
uncovered drawer of the fossil insect collection in
the Museum of Comparative Zoology for 30
years, padded with cotton in a small plastic box
with a snap clasp. Over the years there had been
deterioration of the piece; it become darker and
more fractured, which is typical of even softer,
less brittle amber like Baltic material (Grimaldi,
1993). Cretaceous material is even more susceptible
to oxidative damage. To slow or prevent further
deterioration, Canada Balsam had been applied
to one or more faces of the piece (F M.
Carpenter, personal commun. to DG, 1988), although
when and how often is unknown.
The ant itself was very close (ca. 0.3 mm) to a
flat, prepared surface. This surface had numerous,
fine, parallel scratches, the result of grinding/polishing
by Carpenter or others. On top of this surface
was a layer of clear, hardened material with
a slightly irregular surface, 0.1-0.2 mm thick, that
prevented detailed observation of the holotype. A
cotton swab moistened with 70% ethanol gently
rubbed on the surface resulted in no visible effect.
AMERICAN MUSEUM NOVITATES
Balsam would become tacky under such treatment.
The coating(s) applied just over the ant no
doubt were made to reduce surface distortions for
photography and close examinations. It later became
apparent that this material was almost certainly
dried mineral oil, or perhaps a synthetic
slide mounting medium like Euparol (or both),
based on the manner in which this substance behaved
during curing in a synthetic embedding resin,
and some other observations.
Mineral oil has traditionally been used for extremely
clear observation of inclusions in amber
(e.g., Grimaldi, 1993). F. M. Carpenter used mineral
oil, in fact, to store some pieces of Baltic and
Canadian amber in the MCZ, as a method to prevent
oxidative decomposition, but he also embedded
some pieces in Canada Balsam (Grimaldi,
1993; also see comments below). Lastly, the cotton
stored in the box with the type specimen was
stained yellowish, similar to mineral oil residues
on cotton from specimens in the AMNH collection.
If the layer was even partially dried mineral
oil, numerous coatings must have been applied
over the years, perhaps by various investigators
inspecting the specimen.
To prevent further deterioration of the MCZ
specimen, a process of vacuum embedding in a
synthetic resin was used, refined from that of
Schlee and Dietrich (1970), who developed it for
preserving and studying very brittle Lebanese amber.
The technique not only seals the piece from
atmospheric oxygen, it is an excellent physical
protection from accidental shattering, and is the
only reliable way to trim into a piece of cracked
amber for accurate views of inclusions without
further fracturing or splitting the piece. The technique
has been used successfully and consistently
on over 800 pieces of New Jersey and Lebanese
amber at the AMNH. A detailed, illustrated description
will be presented elsewhere (Silverstein,
and Nascimbene, 1997), but with basic techniques
mentioned here.
The embedding medium is an epoxide (Buehler,
Inc.) that is hardened using a polymerization/catalyzing
agent. Heat is generated during the polymerization;
the larger the volume of medium, the
hotter the reaction. Epoxide and catalyzing agent
are mixed in a separate container, then poured into
shallow cylindrical rubber molds (Buehler, Inc).
The amber piece is then gently slipped beneath
the surface of the liquid epoxy, bubbles removed
from the epoxide, and the preparation placed under
a bell jar that is sealed and brought to approximately
4 psi of pressure (atmospheric pressure
at sea level being 14 psi). The reduced pressure
removes air from fine cracks in the amber,
allowing epoxide to seep into the cracks and bind
fractures together (it also improves visibility, by
eliminating mirrorlike fractures filled with air).
After 10 minutes under vacuum, the rubber cups
are removed and the specimen is allowed to hardened
at room temperature and pressure, generally
taking several hours. The hardened block can then
be trimmed with a water-fed diamond saw and
ground with water-fed emory wheels of 320 and
600 grits.
Shortly after the MCZ piece was removed from
the vacuum, a foam of bubbles suddenly appeared
on the coated surface over the ant, signaling a
reaction within the epoxide no doubt initiated by
the heat of polymerization. Within several minutes
the epoxide had become thickened enough to
prevent removing the amber without damage. Numerous
previous embeddings done in this manner,
using pieces of New Jersey amber and epoxide
volume several times this size, never yielded visible
effects to the amber, let alone a froth of bubbles.
The heat alone from the polymerization reaction
would not cause such an effect on the amber
(amber, in fact, requires temperatures in excess
of 350°F for any softening to occur). The
coating over the ant had caused the intense bubbling,
since uncoated surfaces were largely unaffected.
To our deep disappointment, we found that
the coating had penetrated several millimeters into
the amber.
After the epoxy was completely hardened, it
was trimmed and polished. No view of the ant
could be found, the surface where it now was being
opaque with a suspension of yellowish bubbles.
The block was cut through the middle of the
amber piece, distant from the ant, in an attempt
to view the ant from the other, interior side. (In
cutting through the center, other, minute insects
may have been obliterated, which we considered
worth sacrificing for the sake of the ant. One unusual
psychodid midge deep in the piece, though,
was revealed this way and remains very well preserved
and displayed, a silent and enduring witness).
Cutting through the interior of the amber
exposed highly fractured and brittle amber too
deep for the epoxide to have permeated, even under
vacuum. Both halves were vacuum embedded
again, with perfect results (the coated surface of
the amber was already sealed). Since the exposed
inner surface of the amber was cemented by the
second embedding, grinding of the interior surface
toward the outer surface with the ant could
now be done safely. Reaching 2 mm within the
presumed surface of the ant revealed no specimen.
It was only after a cross section was ground away
from one edge that it became apparent that the
bubbling involved the 1-2 mm of surface amber
containing the ant. During the bubbling of the
coating + amber mixture, the ant had become dis-
NO. 3208 42
GRIMALDI ET AL.: PRIMITIVE ANTS IN CRETACEOUS AMBER
epoxideiIIK
-=-
o o
Fig. 24. Schematic interpretation in cross section
of damaged incurred to the amber piece containing
the type of Sphecomyrma freyi during embedding
process. Top, prior to embedding. Middle,
formation of reaction bubbles. Bottom, end
result. Uncoated surfaces were largely unaffected.
43
articulated and the parts entirely obscured, with
the specimen effectively disintegrated.
What was so stunning was the dramatic and
destructive effect of the coating on the amber itself,
a substance popularly considered inert. The
effect must have been greatly enhanced by oil that
penetrated numerous fine fractures in the piece,
and by presumably 30 years of contact with and
replenishment of oil. If any of these microscopic
and oil-laden fractures extended to the ant, its
body cavity would probably have contained the
coating too. Oddly, Baltic amber stored for decades
in vials of mineral oil at the MCZ showed
little surface degradation (D. Grimaldi, personal
obs., 1995). A small collection of Arkansas amber,
however, given to the AMNH and stored for
20 years in mineral oil at the Univ. Illinois by
Ellis MacLeod, was soft and malleable even to
the core of pieces 20 mm thick, and totally degraded.
Mineral oil obviously has dramatically
different effects on different ambers. Even though
Baltic and Arkansas ambers are similar in age,
they have completely different botanical origin
and chemistry, which must account for the different
reactivity. New Jersey amber is no different.
The fact that this amber visibly reacts with organic
solvents like acetone, whereas most other ambers
(including Cretaceous amber from Lebanon
and Canada) do not, indicates a particularly fragile
and reactive composition.
This preparation is a tragic lesson in the study
and stewardship of valuable amber fossils. First,
the use of mineral oil-almost certainly the coating
that caused the disintegration-must be stringently
avoided. Despite advocacy of the use of
mineral oil for viewing inclusions (e.g., Grimaldi,
1993; Poinar, 1992), this oil clearly chemically
reacts with some ambers much more than others.
Sugar syrup or glycerine, or other water-based
substance, should be used. Hopefully it is not too
late for some specimens. Many pieces of amber
in the Acra collection of Lebanese amber, and
even some of the New Jersey amber ants reported
in this study, had been coated with mineral oil at
various times for better viewing of inclusions.
Thin films of the oil must still reside on the surface
and in the fine cracks.
Secondly, failures like this must temper future
curatorial decisions. Given a particularly valuable
amber fossil that will gradually disintegrate with
age, but which has been treated in unknown ways,
keen insight must be excercised as to the appropriate
method of conservation.
David Grimaldi, Curator, AMNH
Paul Nascimbene, Curatorial Assistant
1997

----- Original Message ----
From: Tom Buckley <tbuck22 at optonline.net>
To: Christopher Albrecht <cjalbrecht at msn.com>; amber at ambericawest.com
Sent: Sunday, March 11, 2007 8:42:36 AM
Subject: Re: Amber Listserv / Amber Care

Chris,

    In your experience, how is this stuff different from the more traditional epoxy resins? Do you still have to pull a vacuum to remove air bubbles and get the resin into all the cracks and crevices? Also, the fact that it's described as biodegradable has me wondering as to how long it will last once used to encapsulate the amber. Sorry for all the questions but the Ward's site doesn't give much info. Thanks.

Tom 

Tom Buckley
Silicone Specialist
Polymer Engineering

Phone: 845-258-4928
Fax: 845-258-4930
----- Original Message ----- 
From: Christopher Albrecht 
To: amber at ambericawest.com 
Sent: Saturday, March 10, 2007 8:14 PM
Subject: Re: Amber Listserv / Amber Care

Hi Everyone:

I have experimented with bioplastic resin. It works wonders with very brittle New Jersey ambers. I embed the piece in the resin and then polish one part back to the amber. The hard resin stablizes the amber. Search the term "bioplastic" online and you will find suppliers. It is expensive also. I got mine from Wards.

This brings me back to a question I asked the list 3 months ago, which noone gave comment to. A lot of time we bag a piece of amber with a paper label. Can paper, which often has an acid content to it, cause amber to change chemically? John, your the chemist... any ideas? I have started to double bag pieces with the label in the second outer bag separate from the amber piece as a precaution. Some pieces of paper in with pieces from the DR and New Jersey chaged color over time from the amber. I did not see this effect with Canadian amber, Burmese or Baltic.

My two cents...

Pax, Chris Albrecht

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